I. Field
The following description relates generally to wireless communications, and more particularly to utilizing an estimate of speed of an access terminal to control power in a wireless communication system.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data can be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, . . . ). For instance, a system can use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Orthogonal Frequency Division Multiplexing (OFDM), and others.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple access terminals. Each access terminal can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to access terminals, and the reverse link (or uplink) refers to the communication link from access terminals to base stations. This communication link can be established via a single-in-single-out, multiple-in-single-out or a multiple-in-multiple-out (MIMO) system.
MIMO systems commonly employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which can be referred to as spatial channels, where NS≦{NT, NR}. Each of the NS independent channels corresponds to a dimension. Moreover, MIMO systems can provide improved performance (e.g., increased spectral efficiency, higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
MIMO systems can support various duplexing techniques to divide forward and reverse link communications over a common physical medium. For instance, frequency division duplex (FDD) systems can utilize disparate frequency regions for forward and reverse link communications. Further, in time division duplex (TDD) systems, forward and reverse link communications can employ a common frequency region so that the reciprocity principle allows estimation of the forward link channel from reverse link channel.
Wireless communication systems oftentimes employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or unicast services, wherein a data stream may be a stream of data that can be of independent reception interest to an access terminal. An access terminal within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, an access terminal can transmit data to the base station or another access terminal.
Transmission of signals over a wireless channel can cause alterations of such signals. For instance, a signal can be transmitted at a first power level and received at a disparate, second power level. The transmit power can be controlled based upon knowledge of the channel (e.g., gain, loss, channel conditions, interference, . . . ) such that receive power is at a desired level. By way of illustration, a base station can control the power level of a transmitted signal to enable an access terminal to receive that signal at a desired power level, thereby allowing the access terminal to further process, store, utilize, etc. a message conveyed by the signal. However, since it is not possible to know the channel state perfectly at any given time, power control is performed based on prior estimates of link quality. Conventional techniques for controlling power at a base station, however, typically fail to account for speed of an access terminal (e.g., which dictates how fast the channel has changed since the last estimate); rather, a common power control algorithm is oftentimes employed for access terminals traversing at different speeds, which can be suboptimal since such scenario leads to designing for worst-case channel conditions.